Hello, 

I needed 300 participants for my experiment. I opened 300 spaces in otree hub room. But now some participants left the experiment without completing it. Can I open some spaces for more participants while the experiment is going on on prolific? 

Best,
Sahar

You can't change the size of a session while it's ongoing. You could close the room and create a new session, but that could disrupt the participants who try to re-access the original start link.

Can I ask what would be your suggestion then? If I wait until all the spaces are filled, can I then close the room and create another session?

you can do that but if participants who already started the experiment go back and re-click on your start link you sent them, they will be taken to a new experiment and be confused.

What is the other option then? Is there anything I can do? Because I already paid the fee on Prolific. 

Actually in the beginning I opened more than 300 spaces. But in the middle of the experiment, I pushed the button of Advance slower users. And when I push that button it shows 20 spaces that never are filled with the joining participants. So, the spaces now are empty but they cannot be filled in with new participants.

Sarah wrote:

> But in the middle of the experiment, I pushed the button of Advance slower users. And when I push that button it shows 20 spaces that never are filled with the joining participants.

Yeah, that is (unfortunately) how the “Advance slowest user(s)” button works: If some participants in a room/session have not even arrived yet, they are considered the “slowest users” and “advanced” to the initial page of your study.

Chris, it would be really great to add “Advance this user” buttons to the “Monitor” page and/or to add an “Advance slowest participant(s)” button that only affects users who have actually started participating in the study.